1. Field of the Invention
The present invention pertains generally to medical devices for cardiac pacing, and more particularly to a pacing lead and associated sheath delivery system. The pacing lead has a tapering body with a thin distal lead shaft and at least one electrode in a configuration that permits increased steerability to enable permanent transvenous pacing of the left ventricle of the heart.
2. Description of the Background Art
The heart, which is an essential organ in the body, rhythmically pumps blood throughout the body so as to supply oxygen and energy to cells. The inability of the heart to maintain proper rhythm, however, can lead to congestive heart failure in which blood backs up into the lungs and/or veins.
Congestive heart failure is a major cause of morbidity and mortality worldwide, with over 350,000 heart failure deaths each year in the United States alone. At any one time an even greater number of Americans are living with advanced congestive heart failure. These numbers are expected to grow as our population continues to age and a larger proportion of Americans are in the older age groups.
Patients with advanced heart failure have markedly increased mortality (20% to 40% per year). In such cases, treatment involves multiple medications. For younger, otherwise healthy heart failure patients, heart transplantation is often considered. Unfortunately, the restricted supply of donor hearts, as well as side effects related to immunosuppressive therapy, severely limit the widespread applicability of this surgical procedure. Therefore, many people will suffer and die with intractable congestive heart failure.
It is well known that pacemakers can be used to reestablish normal cardiac rhythms. A pacemaker consists of two parts: a pulse generator, and an attached lead or leads. The lead includes at least one insulated wire with an attached electrode that transmits an electrical pulse from the pulse generator to the cardiac tissue. Receipt of the output pulse causes depolarization and contraction of cardiac tissue, in a phenomenon termed xe2x80x9ccapture.xe2x80x9d
Most pacemakers operate on demand, so that the output pulse is generated in response to a signal from the lead, which continuously monitors or senses the intrinsic electrical activity of the heart. In contrast, asynchronous pacemakers deliver electrical impulses to the cardiac tissue at a fixed rate.
Pacemakers are commonly implanted in a minor surgical procedure during which the patient is mildly sedated and given a local anesthetic. Through an incision near the collar bone, the pulse generator is implanted under the skin and the leads are inserted into a vein leading to the heart. The leads are then advanced to the heart using continuous fluoroscopic guidance. The electrode is then positioned or fixed within the heart. A lead passed through a vein for fixation within the heart is termed transvenous. Once positioned, the leads are generally not removed.
There are two types of pacemakers: single-chamber, and dual-chamber. Single-chamber pacemakers typically have one lead positioned within the right atrium or right ventricle. Dual-chamber pacemakers (DDD) on the other hand typically have two leads, one positioned within the right atrium and one positioned within the right ventricle.
It has recently been observed that specialized pacing modalities may reduce symptoms and improve the quality of life in patients with advanced heart failure. DDD pacing with shortened atrioventricular (AV) delay is efficacious in patients with endstage idiopathic dilated cardiomyopathy. A symptomatic improvement has been observed, as well as improvement in left ventricular ejection fraction. Other observations include clinical and hemodynamic improvement with shortened AV delay pacing.
Typically, the leads of a dual-chamber pacemaker are placed within the right side of the heart. Under several circumstances, however, simultaneous pacing of both the right and the left ventricle may be desirable. Pacing both ventricles may simultaneously result in a dramatic improvement in clinical status and ventricular function in patients with congestive heart failure. In other circumstances, the right ventricle cannot be safely accessed, and transvenous pacing of the left ventricle may be a desirable substitute. Though rare, access to the right ventricle may be limited because of tricuspid valve stenosis, the presence of a tricuspid valve prosthesis, a congenital heart defect, or as the result of certain surgical procedures.
While left ventricular transvenous pacing is clearly desirable, it is presently unavailable. Left ventricular pacing, on the other hand, is limited to epicardial leads. In one known study, for example, a standard permanent pacing lead was implanted in the right ventricular apex and utilized an epicardial lead for the left ventricle. In contrast to a transvenous lead, an epicardial lead is attached to the outside of the heart, by known fixation methods. Placement of an epicardial lead requires that the surface of the heart be exposed, for example by thoracatomy, and involves considerable operative risk in these already very sick patients.
Currently there are no devices for permanent transvenous left ventricular pacing. Limitations and difficulties in carrying out such pacing include access to the distal cardiac veins, attainment of adequate pacing capture thresholds, and prevention of pacing lead dislodgment. A device designed for such pacing must overcome these obstacles and be simple to use. The device must allow the operator to easily cannulate the orifice of, for example, the coronary sinus. Furthermore, the pacing lead must be designed to allow advancement into selected distal veins at the discretion of the operator. A low profile device is required for cannulation of veins with diameters as small as 1.5 mm or less. Also, the pacing lead must be designed to prevent dislodgment once the desired pacing site has been selected.
The present invention satisfies the foregoing needs, as well as others, and overcomes deficiencies associated with prior devices, thus providing a permanent pacing lead that is useful for transvenous pacing of the left ventricle, particularly in patients with congestive heart failure. In general terms, the present invention pertains to an apparatus and method for permanent cardiac pacing in the distal cardiac veins, particularly the coronary sinus of the left ventricle. The invention is designed to provide a safe, effective, and practical tool for such cardiac pacing.
By way of example, and not of limitation, a device for left ventricular pacing via the distal cardiac veins according to the invention comprises a tapered body of reduced diameter at its distal end, and at least one electrode positioned in the area of the thin distal end of the tapering body. A floppy coil can be attached as an integral part of the tapered body, or provided as a separate component, to serve as a guidewire for steering the pacing lead. Notably, the invention does not include means for securing the distal end thereof to the wall of the heart after placement.
In a first embodiment of the invention, a floppy coil is affixed to the distal end of the pacing lead as a guidewire. A conventional stylet is inserted into the pacing lead for steering, but does not extend into the floppy coil. Here, the floppy coil remains after placement of the pacing lead since it is an integral part of the pacing lead.
In an alternative embodiment of the invention, an integral floppy coil is not provided. Instead, a stylet with a floppy coil at its distal end is provided for steering. In this embodiment of the invention, the tapered body includes a central lumen and a water-tight valve with a central entrance coaxial to the central lumen. The distal end of the coil, and eventually the stylet, is inserted into the proximal end of the tapered body until the coil extends through the center of the water-tight valve and out the distal end of the body. The amount of protrusion can be adjusted to the desired length. The coil is then used as a guidewire to position the pacing lead. When the coil is in position, the stylet/coil assembly can be withdrawn to leave the pacing lead in position. Note, however, that this embodiment also permits xe2x80x9cover the wirexe2x80x9d positioning. In other words, the pacing lead can be moved distally over the coil until the distal end of the pacing lead is in any position along the coil. After placement of the pacing lead, the stylet/coil assembly is retracted. In either placement approach, the valve automatically closes off to make a watertight seal when the stylet/coil assembly is withdrawn.
In accordance with one electrode configuration of the invention, the device comprises a bipolar pacing lead with both a proximal ring electrode and a distal ring electrode, wherein the electrodes each form a cylinder configuration having about 1 mm in height.
In accordance with an alternative electrode configuration of the invention the device comprises a unipolar pacing lead with a distal electrode at or near the distal terminus of the tapering body, wherein the electrode forms a cylinder configuration having about 1 mm in height.
Also provided with the invention is a sheath delivery system for delivery of the pacing lead into the coronary sinus or a distal cardiac vein. Such a delivery system comprises a J-tipped guidewire insertable into the right atrium or right ventricle from a cephalic or subclavian vein, a sheath with preformed curve, and a dilator, wherein the sheath, with the dilator positioned therein, is advancable over the guidewire placed into the right ventricle, the guidewire and dilator thereafter removable to cannulate the ostium of the coronary sinus or a distal cardiac vein, and provide guidance for a pacing lead advancable through the sheath into the coronary sinus.
An object of the invention is to provide a safe, effective, and practical tool for permanent cardiac pacing in the distal cardiac veins.
Another object of the invention to provide means for transvenous ventricular pacing in patients who require cardiac pacing but without transvenous access to the right ventricle.
Another object of the invention is to provide a pacing system which can be used in conjunction with standard pacing leads to transvenously pace the left ventricle synchronously with the right ventricle. Such synchronous pacing is particularly advantageous for patients with congestive heart failure due to idiopathic dilated cardiomyopathy or dilated cardiomyopathy from advanced heart disease.
Another object of the invention is to replace a standard ventricular pacing lead in any patient requiring ventricular pacing.
Another object of the invention is to provide a permanent pacing lead that is useful for transvenous pacing of the left ventricle, particularly in patients with congestive heart failure.
Another object of the invention is to Applicants provide a novel design and method for a pacing lead system that allows permanent transvenous pacing of the left ventricle without opening the chest.